#!/usr/bin/env perl

use strict;
use warnings;

use Tk;
use List::Util 'sum';

my $pie_slice_colours
    = [ map { '#' . $_ } qw{ff0000 ffff00 00ff00 00ffff 0000ff ff00ff} ];
my @pie_data = (
    {
        centre_x => 50, centre_y => 150, radius => 40,
        values => [ 1, 2, 5, 3 ], fills => $pie_slice_colours,
    },
    {
        centre_x => 220, centre_y => 105, radius => 100,
        values => [ 1, 8, 16, 4, 2 ], fills => $pie_slice_colours,
    },
    {
        centre_x => 420, centre_y => 75, radius => 75,
        values => [ 1, 1, 2, 3, 5, 8 ], fills => $pie_slice_colours,
    },
    {
        centre_x => 60, centre_y => 40, radius => 50,
        values => [ 32, 16, 8, 4, 2, 1 ], fills => $pie_slice_colours,
    },
);

my $mw = MainWindow->new;

my $ctrl_F = $mw->Frame->pack(-side => 'bottom');
$ctrl_F->Button(-text => 'Quit', -command => sub { exit })->pack;

my $canv_F = $mw->Frame->pack(-side => 'top', -fill => 'both', -expand => 1);
my $sc = $canv_F->Scrolled(Canvas => -scrollbars => 'osoe',
    -bg => '#ffffff',
    -width => 500, -height => 220, -scrollregion => [0, 0, 500, 220],
);
$sc->pack(-fill => 'both', -expand => 1);
my $canvas = $sc->Subwidget('canvas');

draw_pie(\$canvas, $_) for @pie_data;

MainLoop;

sub draw_pie {
    my ($c_ref, $data) = @_; 

    my @coords = @{_get_pie_coords($c_ref, $data)};

    $$c_ref->createArc(@coords, %$_) for @{_get_pie_slices($data)};

    return;
}

sub _get_pie_coords {
    my ($c_ref, $data) = @_;

    my ($x, $y, $r) = @$data{qw{centre_x centre_y radius}};
    my $h = $$c_ref->cget('-height');

    return [$x - $r, $h - $y + $r, $x + $r, $h - $y - $r];
} 

sub _get_pie_slices {
    my $data = shift;

    my @values = @{$data->{values}};
    my @fills = @{$data->{fills}};
    my $total_values = sum @values;
    my $start = 90; 

    return [
        map {
            my $extent = 360 * $values[$_] / $total_values;
            $start -= $extent;
            +{ -extent => $extent, -start => $start, -fill => $fills[$_] }
        } 0 .. $#values
    ];
}